updateRecordAndSendCsv

public class BatchWithCSVResults implements Database.Batchable<sObject>, Database.Stateful {
    
    private List<String> successRecords = new List<String>();
    private List<String> failedRecords = new List<String>();
    private Integer totalProcessed = 0;
    
    public Database.QueryLocator start(Database.BatchableContext bc) {
        return Database.getQueryLocator([
            SELECT Id, Name 
            FROM Account 
            ORDER BY Id LIMIT 250000
        ]);
    }
    
    public void execute(Database.BatchableContext bc, List<Account> scope) {
        List<Account> accountsToUpdate = new List<Account>();
        
        for(Account acc : scope) {
            try {
                acc.Description = 'Updated by batch';
                accountsToUpdate.add(acc);
                successRecords.add(acc.Id + ',' + acc.Name);
            } catch(Exception e) {
                failedRecords.add(acc.Id + ',' + acc.Name + ',' + e.getMessage());
            }
        }
        
        List<Database.SaveResult> saveResults = Database.update(accountsToUpdate, false);
        
        for(Integer i = 0; i < saveResults.size(); i++) {
            if(!saveResults[i].isSuccess()) {
                failedRecords.add(accountsToUpdate[i].Id + ',' + accountsToUpdate[i].Name + ',' + saveResults[i].getErrors()[0].getMessage());
                successRecords.remove(successRecords.size() - 1);
            }
        }
        
        totalProcessed += scope.size();
    }
    
    public void finish(Database.BatchableContext bc) {
        
        String successCSV = 'Id,Name\n' + String.join(successRecords, '\n');
        String failedCSV = 'Id,Name,Error\n' + String.join(failedRecords, '\n');
        
       
        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
        email.setToAddresses(new String[]{'himanshu.s@hicglobalsolutions.com'});
        email.setSubject('Batch Job Results');
        email.setPlainTextBody('Batch job completed. Total records processed: ' + totalProcessed + 
                               '\nSuccessful updates: ' + successRecords.size() + 
                               '\nFailed updates: ' + failedRecords.size());
        
        Messaging.EmailFileAttachment successAttachment = new Messaging.EmailFileAttachment();
        successAttachment.setFileName('success_records.csv');
        successAttachment.setBody(Blob.valueOf(successCSV));
        
        Messaging.EmailFileAttachment failedAttachment = new Messaging.EmailFileAttachment();
        failedAttachment.setFileName('failed_records.csv');
        failedAttachment.setBody(Blob.valueOf(failedCSV));
        
        email.setFileAttachments(new Messaging.EmailFileAttachment[]{successAttachment, failedAttachment});
        
      
        Messaging.sendEmail(new Messaging.SingleEmailMessage[]{email});
    }
}